Just under a year ago, Nick Tate was busy in a modern office overlooking Green Park in central London, at the very heart of government. Ministers rang him, senior civil servants argued with him and he took daily decisions about AS-level exams and primary school tests that affected every child in Britain. As the Government’s chief adviser on exams and the curriculum, he had a pound;65-million budget. Heads and teachers beat their way to his door to give him their views on the latest government initiative.

Now, clad in a cream summer suit, he sits in the headmaster’s study at Winchester College (fees pound;17,000 a year), founded in 1382 to offer education to poor, bright boys. The room is lined with worn, leather-covered volumes of Livy and William Makepeace Thackeray. His view is of Moberley Court, named after a 19th-century headmaster, and the warm red brick of William Butterfield’s Victorian buildings. Through an archway, the leaves of 200-year-old plane trees rustle close to the spot where a piece of 19th-century graffiti - the name A. Trollope - was recently found scratched on a wall.

He teaches “div”, a Winchester peculiarity unknown to the Qualifications and Curriculum Authority, which he led until last August. It is a non-examined subject that includes English, history (his specialism), divinity, philosophy and current affairs. He watches Winchester College football, a cross between football and rugby, also unique to the school, which has 675 boys.

A few weeks ago, when term was in full swing, he sat on the headmaster’s throne resplendent in his PhD gown for a “medal speaking”, a ceremony the rest of the world calls prize-giving.

It is, he says, very different. Perhaps, the biggest difference is his new perspective on the pressures besetting schools bound by demanding daily routines and the relentless flow of bright ideas from Whitehall. The realisation that even in a privileged independent school, innovation may be hugely disruptive, led to his recent pronouncements that we are “an over-examined society” in the wake of the furore over AS-levels.

“I came from a world of working parties, committees and five-year plans into a flux of activity,” he says. “As a new head, I wanted to say, ‘let’s stand back and reflect on what we are doing’. I was over-ambitious about my ability to keep things going and to cope with some of the reflection and innovation I wanted. I have been struck by how innately conservative schools are. Because the routines are so demanding, there is a tendency for things to roll on and for the status quo to be maintained by vested interests.”

During term, Dr Tate, who is 57, works seven days a week and is on duty 24 hours a day. He starts at 8am, when he sees staff and miscreant boys, and at 8.45am dons his gown and heads for chapel. At 9am, he stands in the courtyard and watches the boys head for class. Then come meetings with committees and the senior management team he has set up. This year, he has taught div to 17 third-year boys (that’s Year 11 to the rest of the world). They have covered Nietzsche, John Stuart Mill, Bruce Chatwin and Primo Levi.

He previously taught for only six years in a direct grant grammar school. He says: “I have enjoyed teaching enormously, although I don’t have enough time to prepare and I haven’t had the detailed frame of reference that the QCA documents say you should have.”

Often, the boys take the opportunity to tackle him about more pressing concerns: why are mobile phones banned and why is Sunday chapel still compulsory?

Later come more meetings - perhaps with prefects, the bursar or other senior staff. Most afternoons he watches sport or pops into the art room or design and technology centre. Most evenings there is a house play or school chamber concert to attend. And there is an endless round of entertaining: old boys, parents and the Winchester establishment, the bishop, whose palace is visible from the college gates, the cathedral’s dean and chapter, the Greenjackets regiment and the judges.

It was a world of which Dr Tate knew little before the college’s warden, Lord Younger, rang out of the blue and asked if he was interested in the job. He was educated at Huddersfield grammar school and taught at De La Salle, a Sheffield direct grant school, before becoming a lecturer in teacher training at Balliol College, Oxford. He is the first head of Winchester not to have attended a public school. This year, just two state school boys will be among the school’s new intake, aged 13. Often there is none, although Dr Tate has started a pound;4million appeal for bursaries for bright students who cannot afford the fees.

Yet the man who in his previous job championed high culture, Shakespeare and an end to moral relativism, and who is author of four history books, looks at home in his surroundings as head of what many regard as England’s most academic school. “It can become a little claustrophobic, meeting the same people all the time. Many staff here have houses elsewhere as well as in college, and we have kept our Surrey house. But I have had no sense of stepping back in time, despite the place’s ancient traditions.”

There are compensations. Though Dr Tate took a pound;6,000 pay cut from the pound;96,000 he earned at the QCA, benefits increase his pensionable salary to pound;98,000. The job comes with a 10-bedroom Georgian house with a cleaner, a gardener and a car. His wife, Nadya, who works for the Open University, is also paid a salary by the school, and his 16-year-old son attends.

The year has had its dramas. In May, he suspended 40 boys for smoking cannabis or drinking alcohol, 11 for up to a week and the rest for a night. “It was a case of balancing the interests of the school against the interests of the boys. It gave me a deeper insight into the adolescent psyche. It is more difficult being 14 or 15 than when I was young.”

On several fronts, he says, “it has been difficult to decide what to accept and what to challenge”. Even his ruling that dogs, including teachers’ dogs, should be banned from the playing fields, following complaints from the grounds staff, provoked a flurry among some of the dons, as the teachers are called.

His decisions to introduce staff training days, review the curriculum and set targets in true New Labour fashion went against the school’s traditions. “There’s a distrust of systems, and a feeling that I have gone in for a bit of management-speak. It’s a very organic school that operates in a personal, informal way and prides itself on having resisted management systems.”

But the curriculum review is under way. The abandonment of GCSE has already been ruled out: the school mixes international GCSEs with those taken by pupils in most schools. Over the summer, Dr Tate will consider opting for the International Baccalaureate, which includes arts, science and philosophy, as other independent schools have done, rather than the AS and A-level system that he helped establish as head of QCA. He is also considering using the intermediate IB for younger pupils.

One of the great pleasures of his new job is the freedom to say what he thinks and the power to bring about change, provided he can carry his staff with him. In his previous role, his freedom to speak out was sharply curtailed by the arrival of the Labour government in 1997. When the QCA advised ministers not to cut back the primary curriculum and he defended the decision publicly, he was taken aside and told he had blotted his copybook. “There was a powerful media manipulation machine and it was made clear that all positive headlines should be ministerial ones.” From then on, the quango was effectively muzzled. “We were more cautious about giving advice that they didn’t want to hear,” he says.

Despite the battles, Dr Tate enjoyed it. “I do miss the excitement of being at the centre of things, talking to ministers, dealing with the national press. I miss the administrative support and having the money to do what we wanted. Administration here is done on a shoestring. Sometimes I need pound;5,000 and have no idea where I’m going to get it from.” But he has no regrets. “This place can be equally exciting and varied. It shows that, even at my age, it is possible to remake yourself. It has been reinvigorating.”